Pressure regulation device for a hydraulic system

ABSTRACT

The invention relates to a pressure regulation device for a hydraulic system comprising at least one generator (30) of fluid under pressure, a hydraulic actuator (28) and a reservoir (32) of fluid under low pressure, and including an electrovalve controlled by a computer and comprising in a casing (9) an electrical coil (10) and a sliding magnetic core (12) controlling a slide valve (16) sliding in a bore provided in a body (18), the slide valve (16) determining two chambers (22, 36) arranged on either side of the slide valve (16) in the bore, the slide valve comprising a hydraulic chamber (40) communicating with the hydraulic actuator (28) and determining a reaction force adding itself to the force produced by the coil (10), against a prestressed resilient means (20). The hydraulic chamber (40) is delimited by a bore (41) made in the slide valve (16), an end part (43a) of a sleeve (43), a rod (42) and a cup (60) for leaktightness between the rod (42) and the bore (41) of the slide valve (16).

The invention relates to a pressure regulation device for a hydraulicsystem.

It is particularly adapted to the braking systems of motor vehicles withantilocking of the wheels when braking. Present antilocking systems use,between a source of fluid under pressure and a receiver such as ahydraulic brake actuator, an electrovalve controlled by a computer interms of signals representative of the rotation of the wheels of thevehicle in order, in a general manner, to release the pressure of thefluid in the hydraulic actuator when the computer detects the imminenceof the locking of a wheel, and then to connect a second source of fluidunder pressure in order to raise the pressure once again, up to a newdetection of imminence of locking, the cycle then renewing itself.Electrovalves of the same type are used in anti-wheelspin systems inorder to generate a pressure in a brake actuator of a driving wheel whenthe computer detects a tendency of this driving wheel to spin, and thento release this pressure when the tendency to spin has disappeared.

The electrovalves used are electrovalves with all-or-nothing operation.However, the antilocking or anti-wheelspin periods wherein cycles asdescribed above follow one another, last for a very short time duringwhich the electrovalve changes state a very large number of times. Thiscauses an unpleasant noise of hammering of the movable part of theelectrovalve.

Moreover, as the system operates in all-or-nothing manner, surges ofpressure appear in the brakes producing poorly controlled transientconditions.

The object of the present invention is to obviate these disadvantages byusing an electrovalve termed proportional ensuring in the user system ahydraulic pressure dependent on the current circulating in the coil ofthe electrovalve in a given range of displacement of the magnetic coreof the electrovalve.

Such an electrovalve then has the advantage of being controllable simplyby causing the current circulating in the coil to vary withoutnecessitating hammering of the movable part; this therefore results in amajor reduction in the pressure surges in the brakes. Furthermore, suchan electrovalve may easily be controlled by a computer producing achopping at variable frequency of a direct current such as is found onboard a motor vehicle, or else a chopping at fixed frequency and withvariable cyclic ratio, the intensity of the current integrated by thecoil then being dependent on the cyclic ratio.

Such an electrovalve is for example described in U.S. Pat. No.4,744,389. However, the electrovalve described in that Document cannotbe arranged in a hydraulic braking system with antilocking of the wheelsbecause of the pressures used, particularly during the energizing of theelectrovalve. In fact, the electrovalve of that Document is designed inorder to function continuously in a system for regulation of arelatively low pressure. This physical limitation therefore prohibitsthe use of such an electrovalve with high pressures in the hydraulicactuator. Furthermore, that electrovalve does not permit the pressure tobe caused to increase linearly when the current decreases linearly inthe coil and vice versa.

One object of the present invention is to produce an electrovalveserving to cause the pressure to vary linearly in terms of the currentin the coil, capable of being energized with a high pressure in thehydraulic system, and which is of simple design and assembly.

The subject of the present invention is therefore a pressure regulationdevice for a hydraulic system comprising at least one generator of fluidunder pressure, a hydraulic actuator and a reservoir of fluid under lowpressure, and including an electrovalve controlled by a computer andcomprising in a casing an electrical coil and a sliding magnetic corecontrolling a slide valve sliding in a bore provided in a body, theslide valve determining two chambers arranged on either side of theslide valve in the bore, the slide valve comprising a hydraulic chambercommunicating with the hydraulic actuator and determining a reactionforce adding itself to the force produced by the coil, against aprestressed resilient means.

According to the invention, the chamber is delimited by a bore made inthe slide valve, an end part of a sleeve, a rod and a cup forleaktightness between the rod and the bore of the slide valve.

The invention will now be described by way of example with reference tothe accompanying drawing in which:

the single FIGURE shows diagrammatically in section an embodiment of adevice according to the present invention in rest position.

It is known that the coil of electrovalves termed proportional, has theessential feature of being capable of providing a substantially constantforce for a given current in a non-negligible range of displacement ofthe magnetic core, of the order of 2 to 3 mm. This feature is generallyobtained by means of a special geometry of the polar parts. This featureis used in the present invention in order to ensure the requiredfunction by modulation of the current circulating in the coil so as toavoid operation with a movable part hammering very rapidly.

In the FIGURE, such an electrovalve can be seen, comprising in a casing8 a coil 10 for energization, a sliding magnetic core 12 provided withits push rod 14. The hydraulic part of the electrovalve is constitutedby a slide valve 16 sliding in a bore of a body 18. A prestressed spring20 is arranged in a chamber 22 for example between a cup 24 integralwith the slide valve 16 and a wall 26 of the body 18 so as to pull theslide valve 16 towards its rest position shown in the FIGURE, bearingagainst a wall 27 of the casing 8 facing the wall 26.

The slide valve 16 is machined so as to be capable of opening or closinga communication between hydraulic actuator 28 connected to a duct 29, asource of fluid under pressure 30 connected to a duct 31 and a reservoir32 in accordance with the systems for regulation of hydraulic pressurein general use. For this purpose, a groove 34 is provided at theperiphery of the slide valve 16.

The two chambers 22 and 36 located on either side of the slide valve 16in the bore are at the same pressure owing to a drilling 38 made in thebody 18. A chamber 40 determines on the slide valve 16 a reaction force.This chamber 40 is formed in a bore 41 of section S1 of the slide valve16, between this bore 41 and a rod 42 of section S2 less than S1.

Between the bore 41 and the rod 42 is arranged a sleeve 43 sliding insubstantially leaktight manner in the bore 41, and wherein slides insubstantially leaktight manner the rod 42. The active end 43a of thesleeve 43 therefore presents an annular surface equal to S1-S2, andcontributes to delimiting of the chamber 40. The latter communicateswith the groove 34 by means of a radial drilling or opening 44 in theslide valve 16.

The sleeve 43 bears against the wall 27 of the casing 8 or against apart 46 integral with the casing 8. The rod 42 is shaped at one end witha recess 48 containing in slightly floating manner a ball 50 cooperatingwith a seating 52 formed on the casing 8 or on the part 46 which isintegral with it. The "floating" mounting of the ball 50 in the recess48 has the object of obtaining a perfect cooperation of the ball 50 withthe seating 52, whatever the defects of concentricity between the bore41, the sleeve 43 and the rod 42 due to the production tolerances.

The slide valve 16 is moreover shaped at its end other than that whichbears the cup 24 with radial apertures 54 intended to receive a pin 56.This pin serves as stop for a sleeve 58 for retaining a seal or a cup 60ensuring the leaktightness between the bore 41 of the slide valve 16 andthe rod 42. A washer 62 bears against the cup 60 and serves as stop fora spring 64 bearing moreover on a step 66 formed on the rod 42. The cup60 thus ensures the leaktightness between the chamber 40 and the chamber36.

It will therefore be seen that the spring 64 serves as return spring forthe ball valve 50-52. It will be seen on the other hand that the cup 60also permits the defects of concentricity between the bore 41, thesleeve 43 and the rod 42 to be taken up. Lastly, it will be seen that,owing to this advantageous arrangement according to the invention, allof the components of the electrovalve are assembled solely by movementsof axial direction, with the exception of the pin 56 which is put intoplace at the completion of assembly in a radial direction, having topass through only a single part, namely the slide valve 16. Theelectrovalve according to the invention is therefore particularly simpleto machine since it does not necessitate strict dimensional accuracy,and simple to assemble, as we have just seen. It is therefore veryinexpensive, and of simple, reliable and silent operation as will now bedescribed.

In rest position, as shown, the source of fluid under pressure 30 is incommunication with the actuator 28 via the groove 34, and the chamber 40is in communication with the actuator 28. The two end chambers 22 and 36communicate with one another and are isolated from the reservoir 32 bythe valve 50 resting on its seating 52.

When the electrovalve is energized, for example in a period ofantilocking of the wheels in the context of the preferred application ofthe invention, first of all the current circulating in the coil producesa force opposing that of the spring 64 in order to raise the ball 50,borne by the rod 42, from its seating 52 and to open the communicationbetween the chamber 22 and the reservoir 32. The push rod 14, incontinuing its action on the ball 50, will next cause the other end ofthe rod 42 to come into contact with the pin 56. At that moment, theforce exerted by the push rod 14 must oppose the force of the controlspring 20 in order to cause the slide valve 16 to move. The force isexerted by the push rod 14 against that of the spring 20 whatever thepressure prevailing in the hydraulic system. This in particular enablesthe electrovalve not to have a substantial electrical consumption. Theopening of the valve 50, 52 and the placing of the chambers 22 and 36 incommunication with the reservoir 32 takes place before the current inthe coil 10 reaches its nominal intensity. Then the intensity beingnominal, the rod 42 is stopped against the slide valve 16 through theintermediary of the pin 56, and the movement of the slide valve 16,against the spring 20, closes the duct 31 thus isolating the source offluid under pressure 30 from the actuator 28. Because of the position ofthe groove 34, the latter communicates with the chamber 36 and,consequently, with the reservoir 32. A release of the pressure of thefluid in the actuator therefore occurs. It will have been understoodthat the movement of the slide valve 16 against the spring 20 isproduced by the current in the coil 10 and is promoted by the hydraulicreaction in the chamber 40 on the reaction surface S=S1-S2 whichproduces a reaction force adding itself to that produced by the coil andopposing that produced by the control spring 20. By reducing theintensity of the current in the coil, the pressure having fallen in theactuator 28, the hydraulic reaction force due to the chamber 40diminishes and the slide valve moves in the other direction, closing thecommunication between the actuator 28 and the chamber 36, and thereforethe reservoir 32, and afterwards re-establishing if necessary thecommunication between the source 30 and the actuator 28 permitting thepressure to rise again in the actuator 28.

If the intensity of the current in the coil is increased, the pressurewill fall again in the actuator 28 since the communication between theactuator and the reservoir 32 via the groove 34 and the chambers 22 and36 will be reopened.

It is therefore found that an increase of the current in the coilresults in a reduction of the pressure of the fluid in the actuator 28.It will then be seen that by modulating, for example by chopping, thecurrent circulating in the coil 10, the slide valve 16 will adopt aposition which is a function of the pressure prevailing in the chamber40, and it will be possible, by judiciously controlling this current, toapply the desired fluid pressure to the actuator 28. In fact, thehydraulic reaction generated in the chamber 40 will automatically openor close the communications between the actuator 28 and the source offluid under pressure 30 and between the actuator 28 and the reservoir 32for each given value of the intensity of the current circulating in thecoil 10. By judicious selection of the reaction section S=S1-S2, it willtherefore be possible to dimension the coil 10 so that the electricalconsumption is as low as possible, taking account of the pressuresinvolved.

Moreover, owing to the arrangement of the sleeve 43, of the slide valve16 and of the rod 42, the device of the invention is particularly simpleto assemble and to dismantle, and therefore to maintain.

Although only one specific embodiment of the invention has beendescribed, it is obvious that a person skilled in the art will becapable of making many modifications to it without going beyond thescope of the invention as defined by the accompanying claims.

I claim:
 1. A pressure regulation device for a hydraulic systemcomprising at least one generator of fluid under pressure, a hydraulicactuator and a reservoir of fluid under low pressure, and including anelectrovalve controlled by a computer and comprising in a casing anelectrical coil and a sliding magnetic core controlling a slide valvesliding in a bore provided in a body, the slide valve determining twochambers arranged on either side of the slide valve in the bore, theslide valve comprising a hydraulic chamber communicating with thehydraulic actuator and determining a reaction force added to the forceproduced by the coil and against prestressed resilient means,characterized in that the hydraulic chamber is delimited by a bore inthe slide valve, an end part of a sleeve, a rod and a cup forleaktightness between the rod and the bore of the slide valve.
 2. Thedevice according to claim 1, characterized in that a radial openingcauses the hydraulic chamber to communicate with a groove provided atthe periphery of the slide valve.
 3. The device according to claim 2,characterized in that the sleeve bears against one of a wall of thecasing and a part integral with the casing.
 4. The device according toclaim 3, characterized in that the sleeve slides in substantiallyleaktight manner in the bore of the slide valve and receives slidably insubstantially leaktight manner the rod.
 5. The device according to claim4, characterized in that the reaction force is exerted on an annularsurface of the end part of the sleeve.
 6. The device according to claim5, characterized in that a spring for return of a ball valve is arrangedbetween the cup and a step of the rod.
 7. The device according to claim6, characterized in that the cup is retained operatively by a pinpassing through radial apertures in the slide valve.
 8. The deviceaccording to claim 7, characterized in that the ball of the ball valveis contained in a slightly floating manner in a recess at one end of therod.